Polycarbonates (PC) are synthetic thermoplastic resins derived from bisphenols and phosgenes, or their derivatives. They are linear polyesters of carbonic acid and can be formed from dihydroxy compounds and carbonate diesters, or by ester interchange. Polymerization may be in aqueous, interfacial, or in nonaqueous solution. Polycarbonates are a useful class of polymers having many desired properties. They are highly regarded for optical clarity and enhanced impact strength, high heat resistance, and relative ductility at room temperature or below.
Acrylonitrile-butadiene-styrene (ABS) polymers are derived from acrylonitrile, butadiene, and styrene monomers. ABS materials generally exhibit excellent impact resistance and toughness. In particular, ABS materials combine the strength and rigidity of the acrylonitrile and styrene polymers with the toughness of the polybutadiene rubber. However, when compared to blends of polycarbonate and ABS, neat acrylonitrile-butadiene-styrene is typically used for applications with less stringent mechanical properties, such as tensile, flexural, heat, and fatigue requirements.
Blends of polycarbonates with ABS (PC/ABS) are amorphous thermoplastic blends that exhibit many desired properties, combining the advantages and/or characteristics of both polycarbonate and ABS. For example, ABS can be incorporated into a polycarbonate blend as an impact modifier, resulting in a PC/ABS blend having high stiffness and impact balance, while maintaining adequate flow for filling out tools with complex geometries. These blends are also known to have a good heat resistance, good processability, weather and ozone resistance, good ductility, electrical resistance, aesthetic characteristics, etc.
These polycarbonate blend compositions are routinely used as substrate parts in various applications, including, but not limited to, in the manufacture of parts for the automotive sector, such as, manufacturing of spoilers, IP-retainers, interior-trim pieces, as well as in furniture applications, where good dimensional stability provides design freedom in complex part assembly.
However, the commonly used polycarbonate blend compositions (PC/ABS blends) can lead to the appearance of the undesired splaying (surface patterns) originating near the gate ends of injection-molded parts. At times the splaying can be so severe that the defects are visible even through a top-coat of paint. As a result, a large amount of molded parts may be rejected. While measures have been put in place to reduce splaying, such strategies have shown only limited success and further add significantly to the processing cost and time.
Incorporation of recycle streams of polycarbonate and/or PC/ABS blends from either post-consumer or post-industrial (PCR or PIR) can reduce manufacturing costs of articles comprising PC/ABS thermoplastic blends. However, the use of currently available recycled content to make high performance engineering thermoplastic products can be problematic since property deterioration with increasing recycle content compared to virgin product is expected, particularly with regard to splaying.
When a recycle stream is added to virgin materials either for cost, productivity or regulatory benefits, the properties generally suffer and the ultimate target so far has been to maintain the properties at an acceptable level in comparison to the virgin materials. For example, a recent paper employed Monte Carlo simulations to study this widely-accepted phenomenon of degradation in properties upon incorporation of recycle. (See, “The Effect of Recycle on the Properties of Engineering Thermoplastics,” DeRudder, J., et al., Plastics Engineering, (2012) 68(8): 26-29).
In order to counteract property deterioration with increasing recycle content, it can be necessary to incorporate additional ingredients to match the properties of the virgin material. For example, in order to obtain acceptable properties of pencil hardness, mechanical performance and fireproof performance in compositions comprising recycle PC/ABS and virgin PC/ABS it was found necessary to add polymethylmethacrylate, fire retardant, flexibilizer, processing agent and toner (see Chinese patent application CN102464876A).
Accordingly, to reduce manufacturing costs of PC/ABS thermoplastic blends, there remains a need in the art for polycarbonate blend compositions containing recycled content with reduced splay without changing key properties mentioned above. Additionally, there also remains a need in the art for methods that enable the manufacture of these polycarbonate blend compositions. These and other advantages are provided by various aspects of the present disclosure.